From the Gospel according to Mark
MK 8:11-13

The Pharisees came forward and began to argue with Jesus, seeking from him a sign from heaven to test him. He sighed from the depth of his spirit and said, “Why does this generation seek a sign?  Amen, I say to you, no sign will be given to this generation.”  Then he left them, got into the boat again, and went off to the other shore.